SYNERGISTIC EFFECTS IN SOLVENT-EXTRACTION SYSTEMS BASED ON ALKYLSALICYLIC ACIDS .3. EXTRACTION OF THE TRIVALENT LANTHANIDES AND YTTRIUM FROM CHLORIDE MEDIA IN THE PRESENCE OF DIALKYL AND DIARYL SULFOXIDES

Dialkyl and diaryl sulphoxides were found to cause synergistic shifts in the pH,, values for the extraction of the trivalent lanthanides and yttrium from sodium chloride media by solutions of alkylsalicylic aci ds in xylene. The extent of the synergistic shift for a given sulphoxi de increases with increasing steric bulk of the alkylsalicylic acid us ed. With the homologous series of dialkyl sulphoxides R(2)SO, where R = n-butyl, n-hexyl, and n-octyl, there is little variation in the size of the synergistic shift for a given alkylsalicylic acid. For a serie s of sulphoxides containing similar numbers of carbon atoms, the exten t of the shift increases with the introduction of alicyclic rings, but decreases when aromatic rings are introduced, for example, in the ord er of R: cyclohexyl > n-hexyl > phenyl, although the effect is not ver y marked. For a given extractant mixture, the pH(50) values decrease f rom lanthanum to samarium and then increase from samarium to lutetium. The separation between the pH(50) values for lanthanum and lutetium i ncreases with increasing steric bulk of both the alkylsalicylic acid ( HA) and the sulphoxide (L), but the separations between adjacent lanth anides are in all cases too small to be of any practical use. Slope-an alysis treatment of metal-distribution data, and measurements of the s olubility of the neodymium-alkylsalicylic acid complex in xylene solut ions of the sulphoxides are consistent with the extraction of a mixed- ligand complex of the type NdA(3)L(2).